Transparent ceramics are useful as optical materials in applications such as host crystals in solid-state lasers, transparent armor, as well in IR windows and domes. YAG, due to its high thermal conductivity, strong crystal fields, and optical transmission over a broad spectral range is an excellent material for these applications.
Prior art methods for manufacture of transparent YAG typically employ processes such as dry pressing and slip casting. In these methods, yttria and alumina powders first are combined in a mill with an organic liquid such as ethanol to make a slurry. Alternatively, YAG powder may be substituted for the yttria and alumina powders. Additives such as dopants, sintering aids, dispersants, surfactants, binders and/or pressing aids may be included in the slurry. For slip casting, the slurry is milled to intimately mix the solids and the organics. The resulting milled slurry then is poured into a slip-casting mold to yield a component formed of the ceramic powder and the organics. For dry pressing, the slurry is dried, crushed, sieved and pressed uniaxially and/or isostatically. The component is heat treated to remove organics and yield a green preform. The green preform then is sintered or hot pressed.
These prior art methods have been used to produce YAG materials that have high transparencies. These methods, however, suffer various disadvantages such as not being able to produce sheets of material that can be formed into thin transparent plates. These methods also suffer from difficulty in forming a compositional gradient of dopant through the sintered, transparent component.
A need therefore exists for a method of manufacture of transparent ceramics such as transparent YAG that avoids the disadvantages of the prior art.